title: Differential toxicities of intraneurally injected mercuric chloride for sympathetic and somatic motor fibers: an ultrastructural study.
abstract: OBJECTIVE
  Mercury is a well-known neurotoxin but the susceptibility of autonomic nerves to mercury poisoning in vivo has seldom been studied. Our previous studies have shown that the hypoglossal nerve in hamsters contains somatic motor and postganglionic sympathetic fibers. The aim of this study was to investigate the ultrastructural changes in the nervous system following intraneural injection of mercuric chloride into the hypoglossal nerve in hamsters.
  
  
  METHODS
  Six adult hamsters were used in this study. After anesthesia, the digastric muscle on the right side was removed and the trunk of the hypoglossal nerve was exposed. Two microliters of mercuric chloride aqueous solution was injected into the main trunk of the hypoglossal nerve at the bifurcation. The contralateral hypoglossal nerve was kept intact and used as the normal control. Animals were allowed to survive for 1 or 3 days and were prepared for ammonium sulfide histochemistry and electron microscopy.
  
  
  RESULTS
  Three days after injection of mercuric chloride solution, almost all unmyelinated sympathetic fibers in the hypoglossal nerve trunk were lost, whereas myelinated somatic axons were spared. Although mercury deposition in the myelin sheaths of neuronal processes was observed in the hypoglossal nucleus, the neuronal somas were intact. By contrast, degenerated neuronal processes and mercury deposition in neuronal somas were frequently found in the superior cervical ganglia.
  
  
  CONCLUSIONS
  This study demonstrated an undue susceptibility of sympathetic fibers to mercury intoxication. The mechanisms that underlie the selective reaction of sympathetic fibers to mercury warrant further investigation.
authors.affiliation: Department of Dentistry, National Taiwan University Hospital, 1 Chang-Te Street, Taipei, Taiwan.
authors.forename: Shih-Jung
authors.initials: SJ
authors.lastname: Cheng
authors.forename: Jang-Jaer
authors.initials: JJ
authors.lastname: Lee
authors.forename: Hao-Hueng
authors.initials: HH
authors.lastname: Chang
authors.forename: Hsin-Ming
authors.initials: HM
authors.lastname: Chen
authors.forename: Meng-Ling
authors.initials: ML
authors.lastname: Chiang
authors.forename: Mark Yen-Ping
authors.initials: MY
authors.lastname: Kuo
authors.forename: Chi-Yu
authors.initials: CY
authors.lastname: Tseng
authors.forename: Sang-Heng
authors.initials: SH
authors.lastname: Kok
mesh_terms: D000320:Adrenergic Fibers / Q000187:drug effects* / Q000648:ultrastructure; D000818:Animals; D006224:Cricetinae; D005728:Ganglia, Sympathetic / Q000187:drug effects / Q000648:ultrastructure; D006651:Histocytochemistry; D007002:Hypoglossal Nerve / Q000187:drug effects* / Q000648:ultrastructure; D008627:Mercuric Chloride / Q000633:toxicity*; D008854:Microscopy, Electron; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000648:ultrastructure*
chemical_list: D008627:Mercuric Chloride